The present invention relates generally to a transmission, and more particularly to a variable speed ratio transmission for transmitting rotational motion from an input to an output at an infinite number of speed ratios within a predetermined range of speed ratios.
Transmissions are commonly used to transmit rotational motions from an input to an output at a variety of speed ratios. Although most transmissions are operable at fixed discrete speed ratios, some conventional transmissions are infinitely variable over a range of speed ratios. Such infinitely variable transmissions are operable at any speed ratio between a minimum speed ratio and a maximum speed ratio. However, most of these conventional infinitely variable transmissions do not permit the speed ratio to be changed while the input and the output are standing still. As a result, when the required input torque becomes too great for the power source providing the torque to the input, the power source may stall and cease powering the transmission. If the transmission is mounted in a vehicle and the speed ratio is set too high so the required input torque is too high for the power source to turn the input, the power source may stall and the vehicle will become immobile. If the speed ratio cannot be changed while the transmission is standing still, the required input torque cannot be adjusted downward thereby preventing the vehicle from overcoming its immobility. Accordingly, a need exists for an infinitely variable transmission that permits the speed ratio to be changed while the input and output are not turning.
Internal parts in some infinitely variable transmissions become worn early in the transmission life. If these worn parts are responsible for transmitting torque from the input to the output, the torque that can be transmitted without slippage is often reduced as the parts wear. As a result, some variable speed transmissions may require early maintenance and/or part replacement so they can adequately transmit torque. In many instances early maintenance or part replacement make infinitely variable transmissions non-viable. Therefore, a need exists for an infinitely variable transmission that automatically adjusts its operation as it wears so it is operable for extended periods of time without slippage or maintenance.